If your business is new and small, chances are you won't be able to get 'credit' for your business without personally guaranteeing it (VISA/MC). And so you'll have to work with whatever personal credit rating you have for a few years.

As for accounts at local suppliers, just set up an account, buy stuff and pay for it when the bill comes. And keep doing that.

When I first started out I had less than desireable credit as well. What I did was to explain this and asked our local dealer that we were planning to deal with at that time if we could give him an installment to help build the credit line. He took $500 and after 30 days when the billing went out and he got a check within 3 days he uped the limit to $600 and so forth. We wound up working together and today he is part of the reason for helping to get our foot thru the door.

I would try your local bank.Feel out which bank wants to help a small business.Try to get a line of credit established in the off season when you don't need it right away.
Also get a good accountant right from the get go.Our accountant has a lot of friends in the banking business and the banks love to see his name on our tax returns.They also keep you out of trouble!
Good Luck

Green Finger - I know this is not an immediate fix - but once you are done,thru,finished with making late payments... get at least 3 or 4 "secured" credit cards. Within a year your credit scores will improve dramatically. Within 2 years you will start getting solicited with unsecured cards.
(emphasis on no more late payments/collections)